Re: [PATCH 5 2/4] Return 32/64-bit dir name hash according to usage type

[Bernd Schubert <bernd.schubert@itwm.fraunhofer.de>]

On 03/05/2012 04:59 PM, Ted Ts'o wrote:
> On Mon, Jan 09, 2012 at 02:21:48PM +0100, Bernd Schubert wrote:
>> diff --git a/fs/ext4/hash.c b/fs/ext4/hash.c
>> index ac8f168..fa8e491 100644
>> --- a/fs/ext4/hash.c
>> +++ b/fs/ext4/hash.c
>> @@ -200,8 +200,8 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
>>   		return -1;
>>   	}
>>   	hash = hash&  ~1;
>> -	if (hash == (EXT4_HTREE_EOF<<  1))
>> -		hash = (EXT4_HTREE_EOF-1)<<  1;
>> +	if (hash == (EXT4_HTREE_EOF_32BIT<<  1))
>> +		hash = (EXT4_HTREE_EOF_32BIT - 1)<<  1;
>>   	hinfo->hash = hash;
>>   	hinfo->minor_hash = minor_hash;
>>   	return 0;
>
> Is there a reason why we don't need to avoid the collsion with the
> 64-bit EOF value as well?  i.e., I think we also need to add:
>
> 	if (hash == (EXT4_HTREE_EOF_64BIT<<  1))
> 		hash = (EXT4_HTREE_EOF_64BIT - 1)<<  1;
>
> 		       			       	  - Ted


Thanks for looking into it, really appreciated!

Yeah, you are right, we also should check for 64-bit EOF. But wouldn't 
be something like this be better?

	/* check for hash collision */
	if(is_32bit_api() ) {
		if (hash == (EXT4_HTREE_EOF_32BIT<<  1))
			hash = (EXT4_HTREE_EOF_32BIT - 1)<<  1;
	} else {
		if (hash == (EXT4_HTREE_EOF_64BIT<<  1))
			hash = (EXT4_HTREE_EOF_64BIT - 1)<<  1;
	}



Or am I over engineering?


Thanks,
Bernd